1. Field of the Invention
The present invention relates to connectors associated with video output, and more specifically to detecting the improper connection of a video monitor to another device having multiple video subsystems.
2. Brief Description of the Related Art
When a conventional system is equipped with multiple video subsystems, users can have difficulty identifying the proper video output from the device to use to establish communication between the device and the monitor. As a result, video monitors can be improperly connected resulting in a “No Video” condition. Lack of video can be particularly troublesome since the absence of video makes it difficult for the user to obtain information regarding the correct connection through the normal information channel, e.g. the video display. More specifically, when a personal computer is equipped with a video graphics array (VGA) port on the computer motherboard and a VGA port on a graphics card, a monitor can be connected to either port. If the monitor is connected to the inactive VGA port, the no information will be displayed. While display information is not normally readily available to a user during start-up, and would be useless if the monitor were connected to the inactive output as described above, some information about display configuration is stored on the system, for example, in the video graphics adapter (VGA) basic input/output system (BIOS).
A VGA BIOS is term referring to a library of functions providing a basic interface to a VGA adapter stored in a non-volatile memory such as a ROM located on an exemplary motherboard, VGA adapter board, or graphics board. The BIOS functions are well established and documented such that most applications and operating systems use the BIOS routines for basic screen I/O. Applications and systems software that directly address video memory can call BIOS routines to initialize state of the VGA.
Early ROM BIOS contained a set of functions for screen I/O on both the Color Graphics Adapter (CGA) and the Monochrome Display Adapter (MDA) until the introduction of the Enhanced Graphics Adapter (EGA) in 1985, and the Video Graphics Array (VGA) in 1987. As adapters have evolved in capability and speed, more BIOS functions have been developed and added to the BIOS.
More recently, the Video Electronics Standards Association (VESA) has defined a set of extensions to the display related routines in the standard BIOS. It should be noted that since the release of the original standard, two major revisions have been released: VBE 2.0—ratified in 1994, and VBE 3.0—ratified in 1998. New features include virtual screen areas and a linear frame buffer. VESA has also defined methods for obtaining information about and controlling the monitor resulting in new corresponding BIOS functions including Display Power Management Signaling [DPMS] and Display Data Channel [DDC]. VBE/DDC for example, allows information about the display to be obtained during a query such as a message sent to the display resulting in the display filling in information in a data structure. The new functions are expected to be included in new releases of the VGA BIOS ROM. Some systems, such as that described in U.S. Pat. No. 6,323,828 B1 issued on Nov. 27, 2001 to Perez, allow for testing of a monitor using the DDC and EDID commands. Earlier systems, such as that described in U.S. Pat. No. 5,448,697 issued on Sep. 5, 1995 to Parks et al., describe the ability to exchange information between a system unit and a display unit using a bidirectional communication channel established therebetween.
Many systems are available for certain types of video detection such as manual detection using switches and the like. In U.S. Pat. No. 6,329,983 B1 issued on Dec. 11, 2001 to Wang for example, a microswitch state is used to detect which of an S and an AV video output are being used. Such a manual method is limited however in that use of a switch involves additional components and is subject to failure. Further, Wang fails to describe when the signal associated with the microswitch can be read and thus a computer system in which the microswitch is used may be required to complete boot up in order to detect the video output.
Other systems such as that described in U.S. Pat. No. 6,346,927 B1 issued on Feb. 12, 2002 to Tran et al., are capable of detecting from which external video input a monitor is being driven based on detection of a sync signal generated by the video adapter.
None of these systems however addresses the need to intelligently determine video parameters such as the active video port and to which output the monitor is plugged. It would be desirable in the art therefore to provide a method and apparatus for resolving problems associated with improper video connection by detecting, for example, to which port a video monitor is connected without the use of switches or the like.